The disclosure of Japanese Patent Application No. 2000-272594 filed on Sep. 8, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates generally to a cylindrical vibration-isolating device which includes an inner metal sleeve and an outer metal sleeve that are disposed in a radially spaced-apart relation with each other and are elastically connected to each other by an elastic body interposed therebetween, and which is interposed between two members of a vibration system for connecting these two members in a vibration-isolating fashion. More specifically, the present invention is concerned with such a cylindrical vibration-isolating device which includes a sealing-rubber member adapted to seal a bore of the inner metal sleeve so that entrance of water or other objects into the bore of the inner metal sleeve is effectively prevented, with the vibration-isolating device is installed between the two members of the vibration system.
2. Description of the Related Art
A cylindrical vibration-isolating device is known as one type of a vibration damping or isolating mount that is interposed between two members of a vibration system for flexibly connecting the two members in a vibration damping or isolating fashion. The cylindrical vibration-isolating device comprises an inner metal sleeve and an outer metal sleeve disposed radially outwardly of an inner metal sleeve with a suitable radial spacing therebetween and an rubber elastic body interposed between and elastically connecting the inner and outer metal sleeves. For instance, this cylindrical vibration-isolating device may be used in an automotive vehicle as a member mount such as a suspension member, a deferential mount, a body mount, a suspension bush or the like.
Generally, the cylindrical vibration-isolating device is installed between one and the other members of the vibration system such that the inner metal sleeve is fixed to the one member by a mounting bolt or rod fixedly formed in the one member and extending through the bore of the inner metal sleeve, while the outer metal sleeve is forcedly pressed into a fixing bore formed in the other member. In this condition, the inner metal sleeve is fastened in its axial direction between the one member and a washer, which are held in pressing contact with opposite axial end faces of the inner metal sleeve, respectively. Therefore, water is likely to enter into the bore of the inner metal sleeve through a gap between the one member or washer and the corresponding end face of the inner metal sleeve, thus causing rust of the device and resultant deterioration of strength or durability of the device.
To cope with this problem, it has been proposed to provide a thin sealing rubber layer on at least the one end face of the inner metal sleeve which is held in contact with the one member, so that the sealing rubber layer is compressed by and between the one end face of the inner metal sleeve and the one member.
However, the sealing rubber layer compressed by and between the end face of the inner metal sleeve and the one member is prone to suffer from fatigue or wear thereof due to a load and sliding frictional force continuously applied thereto. This leads to early deterioration of sealing capability of the sealing rubber layer. It is therefore difficult to ensure a fluid-tight sealing between the end face of the inner metal sleeve and the one member for a long period of time.
Examples of various types of known sealing members for the cylindrical vibration-isolating device are disclosed in JP-U-57-165827. A first example is a sealing projection which is integrally formed on one of axially opposite end faces of the elastic body. A second example is a sealing projection which is independent of the elastic body, and is formed on and protrudes outwardly from an outer circumferential surface of one of axially opposite end portions of the inner metal sleeve. In the first example, since the sealing projection is integrally formed with the elastic body, the sealing projection is affected by elastic deformation of the elastic body. Thus, the sealing projection of the first example is incapable of exhibiting a stable sealing capability. In the second example, since the sealing projection is formed independently of the elastic body, molding of the sealing projection and the elastic body becomes cumbersome. Further, the sealing projection of the second example is likely to suffer from stress concentration at a bonding surface thereof to the inner metal sleeve, thus causing occurrence of cracks in the sealing projection and separation in the interface between the sealing projection and the inner metal sleeve. Thus, the sealing projection of the second example is insufficient in terms of durability.
It is therefore an object of the present invention to provide a cylindrical vibration-isolating device which includes a novel sealing structure capable of preventing entrance of water into a bore of an inner metal sleeve with high stability for a long period of time.
The above object may be attained according to the following modes of the invention, each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the present invention is not limited to the following modes or combinations of technical features, but may otherwise be recognized based on the thought of the present invention that described in the whole specification and drawings or that may be recognized by those skilled in the art in the light of the disclosure in the whole specification and drawings.
(1) A cylindrical vibration-isolating device comprising: (a) an inner metal sleeve; (b) an outer metal sleeve disposed radially outwardly of the inner metal sleeve with a radial spacing therebetween; (c) an elastic body interposed between and elastically connecting the inner metal sleeve and the outer metal sleeve, such that at least one of axially opposite end portions of the inner metal sleeve is located axially outward of the elastic body; (d) a connecting rubber layer integrally formed with and protruding axially outwardly from the elastic body, said connecting rubber layer having a thin-walled cylindrical shape and being secured to an outer circumferential surface of the at least one of axially opposite end portions of the inner metal sleeve; and (e) an annular sealing-rubber member formed integrally with and protruding axially outwardly from a protruding end portion of the connecting rubber layer, the annular sealing-rubber member protruding axially outwardly from a corresponding end face of the inner metal sleeve, the annular sealing-rubber member having a radially inner base portion which has a concave surface and rises from a first axial position on the outer circumferential surface of the at least one of axially opposite end portions of said inner metal sleeve, which first axial position is axially inwardly spaced apart from the corresponding end face of the inner metal sleeve.
In the vibration-isolating device according to the above mode (1) of the invention, the annular sealing-rubber member, which is provided on the outer circumferential surface of the at least one of axially opposite end portions of the inner metal sleeve which is located axially outward of the elastic body, is integrally connected and formed with the elastic body via the connecting rubber layer which is secured to the outer circumferential surface of the at least one of axially opposite end portion of the inner metal sleeve. According to this structure, the annular sealing-rubber member can be simultaneously formed with the elastic body with ease and firmly secured to the inner metal sleeve. Further, the presence of the connecting rubber, which is thin and secured to the outer circumferential surface of the inner metal sleeve, is effective to prevent undesirable transmission of the stress between the elastic body and the annular sealing-rubber member. Accordingly, the present vibration-isolating device is capable of exhibiting both of excellent vibration-isolating characteristics owing to the elastic body and excellent sealing capability owing to the annular sealing-rubber member, with high stability. In this respect, the annular sealing-rubber member protrudes axially outwardly from the corresponding end face of the inner metal sleeve, so that, when the vibration-isolating device is installed between two members of a vibration system, the annular sealing-rubber member is held in pressing contact with one of the two members at a portion radially outward of the inner metal sleeve. This ensures an excellent fluid-tight sealing between the one member and the corresponding end face of the inner metal sleeve.
Further, the radially inner base portion of the annular sealing-rubber member is located axially inward of the corresponding end face of the inner metal sleeve. That is, upon vulcanization of a rubber material for forming the annular sealing-rubber member by using a mold, an annular boundary between the mold and the inner metal sleeve is located at the first axial position on the outer circumferential surface of the at least one of the axially opposite end portions of the inner metal sleeve, which first axial position is axially inwardly retracted or spaced apart from the corresponding end face of the inner metal sleeve. This arrangement is effective to prevent a leakage of the rubber material through the annular boundary to the corresponding end face of the inner metal sleeve. Namely, when a rubber layer is formed on the end face of the inner metal sleeve, the rubber layer is likely to be fatigued or wore due to a load or sliding frictional force which act on the rubber layer when the vibration-isolating device is installed in position between the two member of the vibration system. The fatigue or wear of the rubber layer is prone to cause occurrence of undesirable looseness or gap between the inner metal sleeve and one of the two members to which the inner metal sleeve is fixed. According to the present mode of the invention, however, such an undesirable formation of the rubber layer on the end face of the inner sleeve member is effectively prevented, in other words, the cause of the above-indicated drawbacks is eliminated, thus ensuring a stable sealing capability and a stable installation condition of the vibration-isolating device for a long period of time.
In addition, the radially inner base portion of the annular sealing-rubber member has the generally concave surface. This arrangement is effective to minimize local stress concentration at the bonding interface between the inner metal sleeve and the annular sealing-rubber member, thus preventing occurrence of cracks in the annular sealing-rubber member and separation in the interface between the annular sealing-rubber member and the inner metal sleeve. This arrangement is also effective to ensure strength or durability of a portion of the mold by which the radially inner base portion of the annular sealing-rubber member is defined.
(2) A cylindrical vibration-isolating device according to the above-indicated mode (1), wherein the radially inner base portion of the annular sealing-rubber member rises from the first axial position which is axially inwardly spaced apart from the corresponding end face of the inner metal sleeve by a distance within a range of 0.5 mm-2.0 mm.
In this mode (2), when a rubber material is vulcanized within a predetermined mold for forming the annular sealing-rubber member, a leakage of the rubber material through the boundary between the mold and the inner metal sleeve toward the corresponding end face of the inner metal sleeve is surely prevented, while ensuring strength and durability of a portion of the mold, which portion defines the radially inner base portion of the annular sealing-rubber member.
(3) A cylindrical vibration-isolating device according to the above-indicated mode (1) or (2), wherein the generally concave surface of the radially inner base portion of the annular sealing-rubber member has a radius of curvature which is not smaller than 0.5 mm but not larger than a dimension corresponding to a half of a thickness of the connecting rubber layer.
This arrangement of the mode (3) is further effective to prevent or minimize buckling-like deformation of the annular sealing-rubber member caused by stress concentration at or a load application to the base portion of the annular sealing-rubber member, thus ensuring further improved durability and stability of a sealing capability of the annular sealing-rubber member.
(4) A cylindrical vibration-isolating device according to any one of the above-indicated modes (1)-(3), wherein at least one of an inner and an outer diameter of the annular sealing-rubber member is gradually increased in an axially outward direction toward a protruding end thereof.
This arrangement of the mode (4) is effective to minimize compression stress generated in the annular sealing-rubber member when the vibration-isolating device is installed in position and the protruding end portion of the annular sealing-rubber member is held in pressing contact with the one of two members of the vibration system. This facilitates shear deformation of the annular sealing-rubber member, thus minimizing a possibility of fatigue of the annular sealing-rubber member and resultant decrease in the pressing force of the annular sealing-rubber member acting on the one member. This results in an improved durability of the annular sealing-rubber member.
(5) A cylindrical vibration-isolating device according to any one of the above-indicated modes (1)-(4), wherein the annular sealing rubber has an outer diameter gradually increased in an axially outward direction from a second axial position located axially inward of the first axial position toward a protruding end thereof.
According to this mode (5), a wall thickness of the annular sealing-rubber member is sufficiently increased especially at the base portion of the annular sealing-rubber member, thus minimizing stress concentration at the base portion of the annular sealing-rubber member and improving durability of the annular sealing-rubber member. In this case, a mold for forming the annular sealing-rubber member has a tapered portion that is tapered in a direction in which the obtained annular sealing-rubber member is removed from the mold, thus improving mold-release characteristics.
(6) A cylindrical vibration-isolating device according to any one of the above-indicated modes (1)-(5), wherein the annular sealing-rubber member has a wall-thickness gradually decreased toward a protruding end thereof.
While the base portion of the annular sealing-rubber member is likely to suffer from a problem of local stress concentration, this arrangement of the mode (6) is effective to prevent occurrence of cracks in the base portion of the annular sealing-rubber member and separation in the interface between the inner metal sleeve and the annular sealing-rubber member, thereby further improving durability of the annular sealing-rubber member. In addition, the arrangement of the mode (6) ensures a low spring stiffness of the protruding end portion of the annular sealing-rubber member, so that the protruding end portion of the annular sealing-rubber member is likely to be deformed along the shape of the mounting member, resulting in further stability of sealing capability of the annular sealing-rubber member.
(7) A cylindrical vibration-isolating device according to any one of the above-indicated modes (1)-(6), wherein the corresponding end face of the inner metal sleeve which is surrounded by the annular sealing-rubber member, is formed as a flat annular surface.
According to this mode (7), the inner metal sleeve can be firmly and stably fixed to the one member of the vibration system. This is effective to further improve sealing capability of the annular sealing-rubber member.
(8) A cylindrical vibration-isolating device according to any one of the above-indicated modes (1)-(7), wherein the annular sealing-rubber member is provided only at one of axially opposite end portions of the inner metal sleeve.
In the mode (8) of the invention, the annular sealing-rubber member is provided only one of the axially opposite end portions of the inner metal sleeve. Therefore, the inner metal sleeve may further be provided with a structure for draining water entered the bore thereof from the other end portion thereof. It is noted that the annular sealing-rubber members may possibly be provided at the both end portions of the inner metal sleeve for preventing entrance of water into the bore of the inner metal sleeve from the both ends of the inner metal sleeve. In this case, namely, the both end of the inner metal sleeve are completely sealed by the annular sealing-rubber members. Therefore, the inner metal sleeve may possibly suffer from adverse effect of a negative pressure generated within the bore of the inner metal sleeve due to a change of the ambient temperature. On the other hand, the vibration-isolating device constructed according to this mode (8) is free from such a drawback caused by a generation of the negative pressure within the bore of the inner metal sleeve.
(9) A cylindrical vibration-isolating device according to the above-indicated mode (8), wherein the device is installed in position such that the one of axially opposite end portions of the inner metal sleeve is located above of the other end portion of the inner metal sleeve in a vertical direction.
In this mode (9), entrance of water into the bore of the inner metal sleeve is effectively prevented owing to effect of gravity. Once the water is entered into the bore of the inner metal sleeve, the water can be easily discharged from the bore of the inner metal sleeve, owing to effect of gravity, too.